Acute unilateral hydronephrosis in the setting of hemorrhagic cystitis.

Acute flank pain associated with hematuria and unilateral hydronephrosis is a classic presentation for an obstructing ureteral stone. However, in the setting of hemorrhagic cystitis, blood can acutely obstruct the distal ureter and infrequently result in hydronephrosis. We present a case of an adult female patient with hemorrhagic cystitis who presented with acute right flank pain associated with unilateral hydronephrosis and perinephric fluid on point-of-care ultrasound (PoCUS) in the absence of renal or ureteral abnormality on CT scan hours earlier. Her symptoms resolved, urine cultures showed no growth, and her outpatient follow-up was unremarkable. We suspect given the acute onset of right obstructive uropathy, an unremarkable CT just hours earlier, and the brief nature of her symptoms, that blood obstructed her distal UVJ leading to acute and transient obstructive uropathy.